1. Field of the Invention
The present invention relates to improvement in video signal processing apparatus and method, which convert an interlaced scanning video signal into a progressive scanning video signal. In addition, the present invention relates to a video display apparatus using the video signal processing apparatus.
2. Description of the Related Art
As publicly known, a progressive scanning converter circuit has been developed in order to convert a 2:1-interlaced scanning video signal into a progressive scanning video signal (non-interlaced signal). In order to convert the interlaced scanning video signal into the progressive scanning video signal, scanning lines must be interpolated on every other line. Motion adaptive processing and motion compensation processing have been proposed as the foregoing interpolation.
In the processing described above, there has been proposed a motion-adaptive progressive scanning converter circuit. The converter circuit inputs an input video signal and a video signal before one frame to a motion detection circuit to detect motion from the difference between two video signals. Thereafter, the converter circuit makes the following interpolations in still and moving image (picture) portions in accordance with the motion detection result. In the still image portion, scanning line interpolation (inter-field interpolation) is made using a video signal before one field. In the moving image portion, the means value between neighboring scanning lines is detected from input video signal and a video signal before one line. By doing so, line interpolation (intra-field interpolation) is made.
However, the motion-adaptive progressive scanning converter circuit has the following problems. In the moving image portion, scanning line interpolation is made based on the means value between vertically neighboring scanning lines. For this reason, the vertical resolution is not improved. In the still image portion, scanning line interpolation is made by the video signal before one field, so that the vertical resolution can be improved. However, when still portion moves once, the portion is interpolated based on the mean value between neighboring scanning lines, like the moving image portion. For this reason, the vertical resolution is reduced as compared with the still image state, and also, the degree of reduction is high. As a result, unnatural display video is provided.
On the other hand, there has been proposed a motion-compensation progressive scanning converter circuit, which interpolates scanning lines using frame and inter-field motion vector. Thus, the converter circuit is effective in solving the problems arisen in the motion-adaptive progressive scanning converter circuit. The problems are the reduction of the vertical resolution in the moving image portion and interlace artifact of the moving image portion. However, the motion-compensation progressive scanning converter circuit requires high accurate detection of the motion vector.
JPN. PAT. APPLN. KOKAI Publication No. 5-110997 discloses the following technique. According to the technique, comparison is made between an inter-field interpolation signal moving a pre-field image and a current field image signal based on a detected motion vector. Thereafter, it is determined whether or not the detected motion vector is valid (effective). If it is determined that the motion vector is effective, the inter-field interpolation signal moving a pre-field image is outputted. If it is determined that the motion vector is invalid, an intra-field interpolation signal is outputted.
In this case, whether the motion vector is valid or invalid is determined in the following manner. First, two absolute values are found. One is an absolute value of the difference between a pixel luminance on the current-field scanning line and a pixel luminance on an inter-field interpolated scanning line. Another is an absolute value of the difference between a pixel on the current field scanning line and a pixel on the current field scanning line positioned below one line. The absolute values thus found are compared with a value added in individual blocks. If the difference between two absolute values is smaller than a predetermined threshold value, it is determined that the motion vector is valid. If it is larger than a predetermined threshold value, it is determined that the motion vector is invalid.
According to the technique disclosed in the foregoing Publication No. 5-110997, the intra-field interpolation signal is generated via a vertical low-band filter. However, there is no band limitation with respect to the inter-field interpolation signal. For this reason, difference is generated in a vertical frequency band between these two. As a result, two interpolation signals having different vertical frequency band is changed over at the unit of block in accordance with the determination result of the motion vector. Thus, this is a factor of causing degradation of image quality such that the difference between vertical frequency bands looks like a block in one screen.
According to the technique of the same Publication as above, the current field image signal contains an aliasing distortion component by interlace. For this reason, if correlation is determined based on the interpolation signal and the current field image signal, there is a possibility of making an erroneous determination as to whether the detected motion vector has reliability.
According to the technique of the same Publication as above, whether the motion vector is valid or invalid is determined based on the comparison below. The difference between the current field scanning line and the interpolated scanning lines is compared with the difference signal between current field scanning lines. For this reason, there is a problem that correlation is accurately determined in an obliquely changing image.
JPN. PAT. APPLN. KOKAI Publication No. 2001-24987 discloses the following technique. According to the technique, degradation of a displayed image is reduced even if the detected motion vector is inaccurate. This serves to hold the image quality by motion compensation progressive scanning conversion. JPN. PAT. APPLN. KOKAI Publication No. 2003-32636 discloses the following technique. According to the technique, even if motion vector different from actual motion is detected in motion compensation scanning conversion, high-quality main scanning conversion preventing image degradation is realized. JPN. PAT. APPLN. KOKAI Publication No. 2001-54075 discloses the following technique. According to the technique, motion compensation and motion adaptive interpolation signals are selected in accordance with the reliability of motion compensation processing.
However, the foregoing Publications No 2001-24987, 2003-32636 and 2001-54075 have no any disclosures relevant to the technique of solving the problem described in the Publication No. 5-110997. That is the technique of solving the problem of the degradation of image quality based on the difference in vertical frequency band between intra-field and inter-field interpolation signals.